⟩ Which of the following statement is correct? A. The toughness of a material increases when it is heated. B. The shear stress in a beam varies from zero at the neutral surface and maximum at the outer fibres. C. The stress concentration in static loading is more serious in brittle materials and less serious in ductile materials. D. The stress concentration in static loading is more serious in ductile materials and less serious in brittle materials.